In the field of plant protection, it is known to apply active substances to the plants by spraying or dusting compositions which contain the active substance onto the plants. The active substance acts either by direct contact or systemically, that is, it is absorbed by the plant through the cuticles of the leaves.
The methods heretofore used have some serious disadvantages. On the one hand, there is a clear imbalance between the quantity of active substance required on or in the plant to achieve a positive effect and the quantity of active substance actually applied by spraying or dusting.
On the other hand, the application of plant-protecting substances by spraying or dusting requires certain precautions to prevent damage to the health of anyone present, which cannot always be adhered to particularly in the case of houseplants and horticulture. The storage of large quantities of concentrated active substances constitutes an additional hazard. Moreover, the user, particularly at a domestic or horticultural level, generally finds it impossible to meter the active substance accurately onto the plant. This does not mean the preparation of a solution from a concentrate containing the active substance, but the actual quantity of solution which is sprayed onto the plant. In most cases too much or too little solution is sprayed on. Indoor spraying has the further disadvantage that the immediate area surrounding the plant will also be sprayed with active substance, and consequently the plants should ideally be treated in the open. Any unused left-overs of solution which have evaporated to a crust may cause problems if they cannot be disposed of properly.
A further problem when spraying or dusting is the problem of drifting. In many cases it is undesirable that neighboring plants should come into contact with the active substance. This is the case, for example, if vegetables or fruits ready for harvesting are in the vicinity. It is particularly undesirable for drifting to occur when using systemically acting herbicides, for instance those for combating quack grass.
A further disadvantage of previous methods of application is that after the plant protecting substances have been applied it is no longer readily possible to tell which active substance has been used to treat the plant.